Tubular electrical condensers with overlap seam laminated casing



May 25, 1965 V J. P. SHEEHAN TUBULAR ELECTRICAL CONDENSERS WITH OVERLAPSEAM LAMINATED CASING Filed June 22. 1961 METAL FOIL FIG. 3

mvsmox .JOSEPH P SHEEHAN BY ATTORNEY United States Patent 3,185,759TUBULAR ELECTRICAL CONDENSERS WITH OVERLAP SEAM LAMINATED CASING JosephP. Sheehan, Forest Hills, West Sanford, N.C.,

assignor to Cornell-Dubilier Electric Corporation, a

corporation of Delaware Filed June 22, 1961, Ser. No. 118,855 6 Claims.(Cl. 174-52) The present invention relates to electrical condensers, andto methods of making such condensers; and in particular it relates toimprovements in the enclosin container for condensers and similardevices and its method of manufacture. I r A common form of electricalcondenser includes a wound body of electrodes and dielectric layers, andhas a pair of oppositely projecting wire terminals. The body ordinarilyhas an impregnation of liquid or solid material, and it is enclosed in atube, commonly of impregnated paper or a ceramic, and the ends arefilled with some form of Wax or resin end-fill material, The tubeprovides mechanical protection and contributes to the appearance of theunit. It also is intended to provide vital protection againstpenetration of moisture. The life of a condenser is extendedconsiderably by the effectiveness of its enclosure in sealing outmoisture.

An object of the present invention resides in a new and improvedcondenser having a highly effective moisture-excluding container, and tothe method of making such condensers, more particularly the tubularenclosing portion thereof. The invention has analogous application tocoils, to circuit sub-assemblies and similar devices involving likeconsiderations of providing a protective insulating enclosure that ishighly effective for excluding moisture and at the same time forproviding insulation and mechanical protection. More specific featuresof the invention reside in the provision of a novel tubular case for anelectrical component that incorporates an electrical shield, and inmethods of making such tubular case.

The invention in its various aspectsis disclosed in detail below inconnection with an illustrative embodiment that is shown in theaccompanying drawings, This embodiment involves a condenser body withoppositely projecting terminal wires contained in a tube and sealed byplastic end-fill resin. A film of moisture-impermeable plastic in theform of a tube forms the innermost layer of the tube.

This layer has a surface that is treated to form an intimate 'bond tocurable plastics, such as are used in the later impregnation of the tubeand as the end-fill material. A layer of metal foil covers the plasticfilm and serves both as a shield and as a further moisture barrier thatis insulated from the enclosed condenser body. A wrapping of paper isprovided about the metal foil, the composite tube then being impregnatedwith a rigidizing plastic and cured. Unit lengths of the tube receivecondenser bodies, and end-fill material covers the ends of th condenserbodies and complements the tube in excluding moisture. The end-fillmaterial bonds to the plastic-film layer of the plastic impregnatedtube.

The resulting unit is effectively protected against atmospherichumidity, and it is tough in resisting mechanical shocks. The tube isinexpensive readily fabricated as needed in various sizes, and can beassembled about the functional unit to be protected without subjectingthat unit to excessive processing temperatures such as might be harmfulto the electrical characteristics of the product.

i The nature of the invention, and its further novel fea- 3,185,759Patented May 25, 1965 tnres, objects and advantages will be apparentfrom the following detailed description of the illustrative embodimentshown in the accompanying drawings, wherein:

FIGS. 1 and 2 are diagrammatic illustrations of alternative fabricatingprocedures in the novel manufacture of tubing utilized in theillustrative embodiment; and

FIG. 3 is a diagrammatic longitudinal crosssection of a novelillustrative condenser, the component parts of the enclosure beingexaggerated for more clearly showing the internal construction.

In FIG. 1, one form of tube-winding operation is diagrammaticallyrepresented. Mandrel 10 forms part of a well-known apparatus for makingtubes continuously, such as drinking straws. A plastic strip 12 is drawnfrom a continuous supply of film of suitable width, under roller 14 thatrepresents one part of an adhesive coating apparatus. A strip of metalfoil 16 is similarly drawn from a continuous supply under adhesivecoating roller 18. A strip of kraft paper, suitably colored, is drawnfrom a continuous supply. These three strips are wound in spiral form onmandrel 10, each turn of strip 12 overlapping the previous turn and eachturn of strip 16 overlapping the previous turn. Strips 12 and 16 are ofthe same width, or nearly so, and the overlap seams of the strips 12 and16 are staggered so that a continuous surface of metal foil extendsacross the edge of strip 12, and vice versa. Paper strip 20 is similarlyhelically-wound about the metal- -foil layer, with any desired overlapof each paper layer and the next, or no overlap particularly whereplural paper layers are used, as is desirable.

FIG. 2 represents a modification of FIG. 1. Primed numbers are used inFIG. 2 to designate parts corresponding to those in FIG. 1. In FIG. 2,strips 12 and 16 are laminated to each other, and are wound together,the outer surface of the two layers being adhesive-coated so as toprovide adherence between the overlap regions and adherence for thesubsequently wound paper 20. It is contemplated that a laminated supplyof plastic film and metal foil may be prepared, and handled in thewinding operation as if the laminated strips were a single strip. Inthat case, the coating operation performed by roller 14' would becomepart of the preliminary laminating operation.

FIG. 3 represents an enlarged longitudinal cross-section of a tubularcondenser, including a conventional wound body 22 made of layers ofdielectric strips Wound with metal-foil electrodes (or hearingmetallized-film electrodes) that are separated from each other by thewound dielectric. A terminal wire 24 extends from one such electrode andanother terminal wire 26 extends from the other electrode, and these arerequired to be protected from each other by insulation.

Helically-wound layers of plastic film 12, metal foil 16 and paper strip20 are shown in exaggerated proportions in FIG. 3. Normally a singleunit will have several helical convolutions from end to end; and boththeplastic film and the metal foil are so extremely thin in practice as notto show without exaggeration. The proportions of paper layer 20 are alsoexaggerated, and only one layer is shown although multiple layers, withor without overlap, are used.

The composite tube 12, 16, 20 in FIG. 3 is not merely a short piece oftubing taken from the operation in FIG. 1. The wound tubing is cut toyard-long pieces that are impregnated with a rigidizing curable plastic,which is then heated to effect polymerization. The metal to foil(annealed aluminum foil, for example) and the plastic film aresufficiently supple in the Winding operation so as to be mutuallyconforming, even in the overlap seam areas; but any interstices betweenthese layers that can be reached by the impregnating material, and thespaces in and associated with the paper are also filled with rigidizedplastic; and the impregnating material also coats the inside surface ofthe tube.

The ends of body 22 and parts of terminal wires 24 and 26 are covered byend-fill material 28, 3b, and this end-fill material is bonded to theinside surface of the tube.

A number of commercially available moisture-impervious films aresuitable for use as film 12. For example polyvinyl fluoride film sold byDu Pont under the trademark Tedlar has been used with outstandingsuccess. Fluorohalocarbon film sold by Allied Chemical Company under thetrademark Aclar is also excellent. Other effective films arepolyethylene terephthalate film sold by Du Pont as Mylar; polypropylenefilm as Olefane sold by American Viscose; and polyethylene sold asAlathon by Du Pont. These films are all characteristically very thin,commonly a fraction of .001 inch thick, and they are of unfilledplastic. Fillers generally tend to form moisture-penetrating fissuresthrough the film and surface creepage paths, which would reduce theireffectiveness in excluding moisture.

Each of the films as used is also surface-treated, so as to have surfaceacceptance for bonding to plastics. For surface-treating polyethyleneterephthalate, polypropylene and polyethylene films, the followingtreatment is illustrative: The film is passed through a liquid mixtureof twenty parts by weight of toluene 2,4-di-isocyanate and eighty partsby Weight of orthodichlorobenzene, at 185 F. The vapor phase of toluene2,4-di-isocyanate at 250 F. can be used where the softening point of theplastic will allow, e.g., Mylar and Olefane. Surface treatment ofplastic films is practiced widely and surface-treated films arecommercially available; and such treatments are described in patents andthe literature, no further discussion appears necessary here.

The adhesive coat-ing used may be any of a variety of materials, such asrubber-based adhesives, epoxy-base adhesives, silicones, and polyesters.These all should adhere to both the surface-treated plastic films and tometal foil, as well as paper. They are thermosetting although they mayactually have low cure temperatures, and they are essentially moistureimpervious.

A suitable impregnant is an all hydrocarbon copolymer of butadiene andstyrene containing side vinyl groups as reactive sites for subsequentcross-linking with vinyl monomers to form a thermoset resin. Thematerial is impregnated into the yard-long tubes, which is then heatedto effect setting and hardening, and the hard lengths of tube are cutinto short pieces as required by the condenser to be encased. Any numberof epoxy-based and other impregnants can also be used, excluding onlythose that are subject to moisture absorption.

Numerous suitable thermosetting end-seal formulations may be used at endseals 28 and 3d. Epoxy resin with various fillers and a desired amountof hardener have been used successfully. Normally the filler in thiscomposition should be such as not to impair the insulating properties ofthe end-fill, since the end fill may extend across the cut edges at eachend of the tube where the metal foil is exposed. However, it is ofadvantage in some applications to use a filler in the formulation forthe end fill at only one end of the condenser such that the end fill isrelatively conductive and thereby connects the terminal wire at that endto the shield represented by the metal foil in the encasing tube. Forexample, powdered lead or lead oxide may be used in a conductive epoxyend-seal filler, and in that event the metal foil is advantageously oflead.

ail

The tube-encased condenser above has numerous attributes and uniquecombinations of advantages. The moisture resistance far exceeds that ofsimilar impregnatedpaper encased condensers, and remarkably comparesfavorably with ceramic-tube condensers in this respect. Unlike ceramictubes, the present tubular condensers are not subject to cracking andthey can be attractively colored and labeled in a way that far surpassesthe limitations of ceramic tubulars. The novel condenser incorporates ashield, and yet does not have any appreciable hazard of accidentalshort-circuiting such as might be caused by an exposed-metal shield.Even were the end-seal material limited so as to expose the foil edgesat the ends of the unit, there is only remote possibility of the foilcausing a short-circuit.

It is apparent that the novel features of the foregoing disclosure arereadily susceptible of varied application and modification by thoseskilled in the art, and therefore the invention should be broadlyconstrued in a manner consistent with its full spirit and scope.

What I claim is:

1. An electrical circuit component including a body having projectingterminal wires and an encasing tube, said encasing tube including anunfilled plastic-film tube having overlap seams joined by amoisture-impervious adhesive, and a rigidized and impregnated externalcovering of paper on said plastic tube, and a cured-resin endfillcovering each end of said body and bonded to the inner surface of saidtube.

2. An electrical circuit component including a body having projectingterminal wires and an encasing tube, said encasing tube including anunfilled-plastic-film tube, a complete external metal-foil coveringadhered to said plastic-film tube with a moisture-impervious adhesive,and a rigidized and impregnated external covering of paper on saidfoil-and-plastic tube, and a cured-resin end fill covering each end ofsaid body and bonded to the inner surface of said tube.

3. An electrical circuit component including a body having oppositelyprojecting terminal wires and an encasing tube, said encasing tubeincluding an unfilledplastic-film tube, a complete external metal-foilcovering adhered to said plastic-film tube with a moisture-imperviousadhesive, and a rigidized and impregnated external covering of paper onsaid foil-and-plastic tube, and a cured-resin end fill covering each endof said body and bonded to the inner surface of said tube, the end-fillat only one end of said encasing tube being of an electricallyconductive composition, and extending to the edges of the metal-foillayer in the encasing tube.

4. An electrical condenser including a condenser body having oppositelyprojecting terminal wires and an encasing tube, said encasing tubeincluding an unfilledplastic-film tube, a complete external metal-foilcovering adhered to said plastic-film tube, and a rigidized andimpregnated external covering of paper on said foil-andplastic tube, anda cured-resin end-fill covering each end of said body and bonded to theinner surface of said tube.

5. An electrical condenser including a condenser body having oppositelyprojecting terminal wires and an encasing tube, said encasing tubeincluding an unfilledplastic-film tube having overlap seams adheredtogether by moisture-impervious cement, and a rigidized and impregnatedexternal covering of paper on said plastic tube, and a cured-resinend-fill covering each end of said body and bonded to the inner surfaceof said tube.

6. An electrical condenser including a condenser body having oppositelyprojecting terminal Wires and an encasing tube, said encasing tubeincluding an unfilledplastic-film tube having overlap seams adheredtogether by moisture-impervious cement, a complete external metal-foilcovering adhered to said plastic-film tube with a moisture-imperviousadhesive, and a rigidized and impregnated external covering of paper onsaid plastic tube,

5 and a cured-resin end-fill covering each end of said body and bondedto the inner surface of said tube, the end-fill at only one end of saidencasing tube being of an electrically conductive composition, andextending to the edges of the metal-foil layer in the encasing tube.

References Cited by the Examiner UNITED STATES PATENTS 2,103,841 12/37Calvert 156-53 2,106,850 2/38 McCulloch 156-53 2,203,232 6/40 Osborne156-53 2,298,748 10/42 Brown 156-55 2,549,770 4/51 Burnham 317-2602,597,338 5/52 Kohring 174-52 X 6 Dorst 317-258 X Richardson et a1.156-55 X Allison 317-260 Horowitz 156-195 X Ebel 156-55 Clemons 29-2542Allison 317-260 Hogue 317-260 Dokuchitz et a1. 29-2542 JOHN F BURNS,Primary Examiner.

BENNETT G. MILLER, JOHN P. WILDMAN, E.

JAMES SAX, Examiners.

1. AN ELECTRIC CIRCUIT COMPONENT INCLUDNG A BODY HAVING PROJECTINGTERMINAL WIRES AND AN ENCASING TUBE, SAID ENCASING TUBE INCLUDING ANUNFILLED PLASTIC-FILM TUBE HAVING OVERLAP SEAMS JOINED BY AMOSISTURE-IMPERVIOUS ADHESIVE, AND A RIGIDIZED AND IMPREGNATED EXTERNALCOVER-